Given that crops and livestock thrive in a relatively
narrow set of environmental parameters, it makes sense to explore how climate
change will affect agricultural productivity. Factors considered include the
impacts of rising temperatures, increased production of carbon dioxide and
other greenhouse gases, water supply fluctuations, soil quality variations,
sea-level increases, and the introduction of new pests, diseases, and weeds,
which could hurt agricultural output. These changes can have different impacts
depending on the geographic scale of analysis. Climatic change will have different
manifestations at local, regional, and global scales. Impacts will also vary
according to the agricultural products under consideration. Some plant or animal
species may be very resilient to environmental changes. Others may not adapt so
well to change.
Temperature increases will affect crop and livestock production
in various ways. A warming climate will extend the frost-free growing season at
higher latitudes. Regions that are too cold to support commercial agriculture
in northern Canada, Alaska, Scandinavia, and Russia, may become viable
agricultural areas if temperatures increase. On the other hand,
temperature-sensitive crops may no longer be commercially viable in regions
that become too hot or dry. Also, rising temperatures could increase the heat
stress on livestock.
Climatic change models predict that regional
temperature variations may alter precipitation patterns and the supply of water
for agriculture. Areas that are currently too dry may receive more moisture in
the future. Areas that are productive now without irrigation may suffer as
temperatures increase, because of increased plant evapo-transpiration. Farmers
will have to find ways to offset the rising temperatures and corresponding
moisture loss if they are to survive. Furthermore, many meteorologists suggest
that weather events such as thunderstorms, tornados, and hurricanes may become
more intense and occur with greater frequency. This may bring more rain to some
regions. On the other hand, severe storms cause strong winds and flooding,
which could cause largescale crop damage.
Many regions of the world, such as the Indian Subcontinent,
the Andes region of South America, Kazakhstan, California, and the American
High Plains, rely on melt water from glaciers and heavy winter snows to feed streams
and rivers that provide water for irrigation. These high altitude water sources
have traditionally been viewed as renewable resources that can be depended upon
to provide moisture during the growing season and are then replenished by snow
falls during the frigid winters. However, rising temperatures have caused glaciers
to shrink or disappear and have been linked to reduced snow pack at high
altitudes.
A related problem is that many of the most productive rivers
to fuel hydroelectricity are fed from the melt water of high altitude glaciers
and snow pack. The Yangtze River in China is important for agriculture, and
with the Three Gorges hydroelectric power plant, it is also an important energy
producer. However, the Yangtze River, like the Colorado River in the United
States and the Ganges River in India, is replenished by melt water from
glaciers and snowmelt. This shows the complex impacts of rising temperatures that
will reduce water for agriculture, but also produce a renewable form of energy
to offset carbon dioxide production from fossil fuels. Melting glaciers may
also increase sea levels, which could jeopardize agriculture by flooding and
accelerated soil erosion in many low-lying areas around the world.
Global warming is caused by increased concentrations of
carbon dioxide, nitrous oxides, methane, and other gases produced by the
combustion of fossil fuels. The impact of having more carbon dioxide in the
atmosphere is difficult to gauge with certainty. Plants consume carbon dioxide
in the production of oxygen through photosynthesis. Theoretically, increased
levels of carbon dioxide could spur plant growth because increased atmospheric
concentrations of carbon dioxide mean that there is more available for plants to
use during photosynthesis. In addition, there is a synergistic relationship
between carbon dioxide and water uptake. Plants are more efficient users of water
as ambient concentrations of carbon dioxide increase.
Unfortunately, there are many factors that could offset
the potential productivity gains to agriculture from increased carbon dioxide
concentrations. The conditions that increase the growth of commercial crops
also increase the growth of traditional weeds and could accelerate the growth
of new invasive plant species. Also, increased temperatures will prompt the
growth of plant diseases and insects. In order to reduce the impact of pests
and pathogens, farmers will have to apply more pesticides, herbicides, and other
chemicals, many of which are manufactured from petrochemicals.
Soil dynamics will also be affected by changing temperature
regimes. Rising temperatures will increase the rate at which organic material
decomposes and possibly decrease the level of moisture in soils. This will
lower soil productivity, thus prompting the increased use of fertilizers. This
might be mitigated, though, by the growing presence of nitrogen oxides that are
also increasing as a result of fossil fuel combustion. Increased temperatures
might also accelerate soil erosion in agricultural areas, rising temperatures
increase the severity of thunderstorms. Without appropriate adaptation by
producers, soil erosion could accelerate as the increased flow and force of
water droplets dislodge soil. This is a problem because soil erosion is itself
a cause of carbon dioxide release into the atmosphere.
BIBLIOGRAPHY.
Consultative Group on International
Agricultural
Research, www.cgiar.org (cited
September 2007);
Thomas Lyson, Civic
Agriculture: Reconnecting Farm, Food
and
Community (University
Press of New England, 2004);
Patrick Michaels and Robert
Balling, The Satanic Gases:
Clearing
the Air about Global Warming (Cato Institute,
2000); National Sustainable
Agriculture Information Service,
www.attra.ncat.org (cited September
2007); Monte
Oneal, et al., “Climate Change
Impacts on Soil Erosion
in Midwest United States with
Changes in Crop Management,”
Catena
(v.61, 2005); Organisation for Economic
Co-operation and Development,
www.oecd.org (cited
September 2007); Agnes Sinai,
“China: The Sky Darkens,”
Le
Monde Diplomatique (April
2006); U.S. Department of
Agriculture, www.usda.gov (cited
September 2007); U.S.
Energy Information Administration,
www.eia.doe.gov
(cited September 2007); U.S.
Environmental Protection
Agency, www.epa.gov (cited
September 2007); Matthew
Wald and Alexei Barrionuevo, “The
Energy Challenge: A
Renewed Push for Ethanol, Without
the Corn,” New York
Times
(April 17, 2007); World Bank,
www.worldbank.org
(cited September 2007).
Christopher
D. Merrett
Western
Illinois University
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